Thermic lances were developed following the Second World War as a means by which gun emplacements, submarine pens and other large concrete structures could be broken up or demolished quickly and conveniently.
Operation of a thermic lance usually involves feeding gaseous molecular oxygen through a length of steel tube, the tip of which has previously been heated to combustion temperature. The oxygen combines with the iron in the steel of the lance to form a slag that is rich in iron oxides. The slag produced is very hot and very fluid thus enabling the lance to be used as a cutting and/or boring tool. The flow of slag is assisted by the velocity of the gas and the vapours expelled within it.
The lance is usually packed with steel rods such that the ratio of iron to oxygen is increased thus providing sufficient heat to melt concrete (the melting point of which is between 1800 to 2500° C.) and/or ferrous or non ferrous metals. The heat output of a lance may be increased by adding aluminum and/or magnesium to the packing. Smaller lances have been packed with a roll of sheet steel in place of steel rods.
Examples of thermic lances are disclosed in, for example, U.S. Pat. No. 3,570,419 (Brandenberger; published 1971), U.S. Pat. No. 3,738,288 (Brandenberger; published 1973) and GB-A-2151530 (Partington; published 1985)
A thermic lance is usually ignited by heating the tip of the lance to the combustion temperature using an oxy-acetylene torch. The tip may also be heated to the required temperature by shorting the tip over a car battery. Either way, once heated, oxygen is then fed through the lance promoting fusion at the lance tip. The combustion reaction is self-supporting and will continue until either the flow of oxygen is stopped or all of the fuel from steel has been consumed. The lance itself is obviously consumed during operation.
The use of an oxy-acetylene torch or a car battery to ignite the lance is not necessarily convenient in all circumstances. In addition, the use of fuel gases with an oxy-acetylene torch is potentially dangerous. The Lance Igniter Tube (or “LIT”) process (Australian Thermic Lance Company) has been developed as a safer way to ignite thermic lances. The process involves the use of a Lance Wick and a Lance Igniter Tube. Once lit, the Lance Wick smoulders slowly. The lance is placed over the LIT tube and the smouldering wick is placed in the same position. Oxygen gas is fed through the lance at low pressure and the wick flares into flame and ignites the LIT tube. The lance is moved into the LIT tube and the oxygen gas flow increased to cause a fierce flame which heats up the end of the lance to the point of ignition.
Ignition of a thermic lance using the LIT process requires two people and, thus, is not convenient if a second person is not available.
U.S. Pat. No. 4,055,332 (Sweeney; published 1977) discloses a thermic lance having a plastic igniter unit for igniting the tip of the lance. The plastic igniter unit is ignited using an electrically ignitable ignition element such as an electric match or an electric squib. The lance is ignited by igniting the igniter unit in a flow of oxygen through the lance.
U.S. Pat. No. 5,622,672 (Swick et al; published 1997) discloses a thermic lance having a chemical igniter unit for igniting the tip of the lance. The unit is sealed and contains a pyrophoric material which spontaneously ignites in a flow of oxygen. The unit is pierced by the lance when struck against a hard surface and the lance is ignited by then passing oxygen through the lance.
U.S. Pat. No. 4,915,618 (Brandin; published 1990) discloses a thermic lance having a chemical igniter unit which is actuated under the pressure of oxygen. The igniter unit includes a primer composition (e.g. iron thermite) and a friction sensitive primary explosive which is used as a primer. A frictional element such as a wire spring is embedded within the primer. A flow of oxygen through the lance causes the frictional element to be blown out of the primer thereby igniting the primer which in turn ignites the primer composition and then the lance.
The lances of U.S. Pat. No. 5,622,672 and U.S. Pat. No. 4,915,618 have particular application for underwater use.
Objectives of preferred embodiments of the present invention therefore include:
providing a thermic lance that may be ignited more safely, more simply and more conveniently by one person; and
providing a thermic lance that may be ignited from a safe distance, e.g. remotely.
Conventional fireworks involve the use of dangerous, explosive and toxic materials. For example, the primary explosive in a firework is usually black powder which is a well known mixture of charcoal, sulfur and potassium nitrate in particular proportions. The products from exploding black powder include smoke, pollutant gases such as sulfur dioxide and sodium and potassium ions which can destroy or sicken non-salt tolerant plants. In addition, the colouration in a firework is usually provided by metal chlorates and/or perchlorates which are usually highly toxic.
A further objective of preferred embodiments of the present invention therefore include providing a safer and more convenient alternative to conventional fireworks.